Julian Fitzell wrote:
> Did anybody ever figure out what the heck is causing this? It's
> driving me nuts!!

It's users of Sensor>>mouseButtons, Sensor>>shiftPressed etc. The main 
suspect in this regard is TransferMorph which does this:

TransferMorph>>step
	self shouldCopy: Sensor shiftPressed.
	self updateCopyIcon

A lingering TransforMorph (which can happen after DnD errors) will 
happily eat all your events.

One thing you can try in such a situation is to see whether there is a 
TransferMorph hidden somewhere. In addition you could just do a stack 
dump whenever someone calls flushNonKbdEvents:

EventSensor>>flushNonKbdEvents

	WorldState addDeferredUIMessage:
		(MessageSend
			receiver: Transcript
			selector: #show:
			argument: thisContext longStack).

[no block in the above since you need the stack eagerly]

Cheers,
   - Andreas